Node apparatus, route control method, route computation system, and route computation apparatus

ABSTRACT

A node apparatus wherein when a topology change occurs on a network used for packet transfer between node apparatuses, the node apparatus performs dynamic route control for establishing a new normal route. The node apparatus has a device that receives, from another node apparatus, a route control message which includes information required for route determination; a device that computes a route on the network based on the received route control message; a device that sends another node apparatus a route control message which includes information required for said another node apparatus to determine a route on the network; a device wherein when receiving the route control message, this device computes an operation start time for route control operation by the route computation and the message sending, based on a distance between a topology change part and said node apparatus of oneself; and a device that controls the execution of the route control operation based on the computed operation start time.

The present application is the National Phase of PCT/JP2009/006020,filed Nov. 11, 2009, which claims priority based on Japanese PatentApplication No. 2008-295928, filed Nov. 19, 2008, the contents of whichare incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a network system which directlyperforms route control, and specifically relates to a node apparatus, aroute control method, a route computation system, and a routecomputation apparatus.

BACKGROUND ART

Accompanied with the spread of network techniques represented by theInternet, improvement in reliability for each network is a pressingneed.

In recent years, reliability for a network has been improved byperforming dynamic route control after preparing a redundant structureincluding node apparatuses and links for the network. In the networkwhich executes the dynamic route control, the node apparatuses whichform the network exchange information about connection statuses thereof.Based on such information, an optimum route is autonomously determined.

For example, if a node apparatus detects a failure in a link connectedto the node apparatus or a node apparatus adjacent thereto (accordingly,a topology change) occurs, the node apparatus which detects the failurecommunicates the failure to other node apparatuses. Accordingly, allnode apparatuses within the network perform route computation withoutconsidering the damaged node apparatus or link, so as to determine a newroute.

As described above, even if a failure occurs, the dynamic route controlmakes it possible to continue the communication service using only theremaining node apparatuses and links.

In order to implement such dynamic route control, a standardizationorganization IFTF (Internet Engineering Task Force) defines standardizedroute control protocols such as BGP (Border Gateway Protocol)-4 (forexample, see Non-Patent Document 1), OSPF (Open Shortest Path First)(for example, see Non-Patent Document 2), and RIP (Routing InformationProtocol) (for example, see Non-Patent Document 3).

PRIOR ART DOCUMENT Non-Patent Document

-   Non-Patent Document 1: Y. Rekhter, T. Li and S. Hares, “A Border    Gateway Protocol 4 (BGP-4)”, RFC 4271, pp. 1-6, Internet Engineering    Task Force, 2006.-   Non-Patent Document 2: J. Moy, “OSPF Version 2”, RFC 2328, Internet    Engineering Task Force, pp. 1-3, 1998.-   Non-Patent Document 3: G. Malkin, “RIP Version 2”, RFC 2453,    Internet Engineering Task Force, pp. 1-4, 1998.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

In order to shorten the service stop time due to occurrence of afailure, the node apparatus which detected the failure must communicatethe failure to all nodes within the network as soon as possible. In thiscase, each node apparatus which receives the failure notification shouldalso transfer the notification as soon as possible.

However, in the above-described Non-Patent Documents 1 to 3, when eachnode apparatus performs such an operation in the network, the loadimposed on each node apparatus temporarily increases. When the load ofeach node apparatus increases due to the route computation, the nodeapparatuses cannot perform the other processes, so that it may notfunction as a node apparatus itself. Therefore, an increase in theprocessing load may affect the stability of the network.

In order to prevent such an increase in the load of each node apparatus,a various types of timer is used, which may be a transfer timer formanaging a time measured from the reception of the notification to thetransmission of the notification to an adjacent router or a computationstart timer measured from the notification reception to the start of theroute computation.

When the above-described temporary increase in the load for the route isprevented by setting such a timer to a relatively large value, thestability of the network can be improved. However, as a result, theservice stop time due to the failure occurrence increases.

That is, the service stop time and the stability of the network have atrade-off relationship, and they are not easily compatible.

In light of the above circumstances, an object of the present inventionis to provide a node apparatus, a route control method, a routecomputation system, and a route computation apparatus, which can shortenthe service stop time without damaging the stability of the network.

Means for Solving the Problem

In order to solve the above-described problem, the present inventionprovides a node apparatus wherein when a topology change occurs on anetwork used for packet transfer between node apparatuses, said nodeapparatus performs dynamic route control for establishing a new normalroute, and said node apparatus comprises:

a message receiving device that receives, from another node apparatus, aroute control message which includes information required for routedetermination;

a route computing device that determines a route on the network based onthe received route control message;

a message sending device that sends another node apparatus a routecontrol message which includes information required for said anothernode apparatus to determine a route on the network;

a delay computing device wherein when receiving the route controlmessage by the message receiving device, the delay computing devicecomputes an operation start time for route control operation executed bythe route computing device and the message sending device, based on adistance between a topology change part and said node apparatus ofoneself; and

an execution control device that controls the execution of the routecontrol operation by the route computing device and the message sendingdevice, based on the operation start time computed by the delaycomputing device.

In order to solve the above-described problem, the present inventionalso provides a route control method wherein when a topology changeoccurs on a network used for packet transfer between node apparatuses,the method is used for establishing a new normal route, and said methodcomprises:

a receiving step that receives a route control message which includesinformation required for determining a route on the network;

a route computing step that determines the route on the network based onthe received route control message;

a sending step that sends a node apparatus a route control message whichincludes information required for said node apparatus to determine aroute on the network;

a delay computing step wherein when receiving the route control message,the delay computing step computes an operation start time for thedetermination of the route on the network and the sending of the routecontrol message, based on a distance between a topology change part anda node apparatus of oneself; and

an execution control step that controls the execution of the routedetermination and the route control message sending, based on thecomputed operation start time.

In order to solve the above-described problem, the present inventionalso provides a route computation system which operates in an autonomoussystem, and includes a node apparatus and a damaged part estimatingapparatus which are connected via an internal network within theautonomous system, wherein:

when a topology change occurs on a network used for packet transferbetween node apparatuses, the route computation system performs dynamicroute control for establishing a new normal route;

the damaged part estimating apparatus comprises:

-   -   a damaged part estimating device that estimates a topology        change part; and    -   a damaged part communicating devise that communicates the        topology change part estimated by the damaged part estimating        device to the node apparatus; and

the node apparatus comprises:

-   -   a message receiving device that receives, from another node        apparatus, a route control message which includes information        required for determining a route on the network;    -   a damaged part receiving device that receives the topology        change part from the damaged part estimating apparatus;    -   a route computing device that determines the route based on the        received route control message;    -   a message sending device that sends another node apparatus a        route control message which includes information required for        said another node apparatus to determine a route on the network;    -   a delay computing device wherein when receiving the route        control message by the message receiving device, the delay        computing device computes an operation start time for route        control operation executed by the route computing device and the        message sending device, based on a distance between the node        apparatus of oneself and the topology change part received by        the damaged part receiving device; and    -   an execution control device that controls the execution of the        route control operation by the route computing device and the        message sending device, based on the operation start time        computed by the delay computing device.

In order to solve the above-described problem, the present inventionalso provides a route computation system which operates in an autonomoussystem, and includes a node apparatus and a distance estimatingapparatus which are connected via an internal network within theautonomous system, wherein:

when a topology change occurs on a network used for packet transferbetween node apparatuses, the route computation system performs dynamicroute control for establishing a new normal route;

the distance estimating apparatus comprises:

-   -   a distance estimating device that estimates a distance between        the node apparatus and a topology change part; and    -   a distance communicating devise that communicates the distance        estimated by the distance estimating device to the node        apparatus; and

the node apparatus comprises:

-   -   a message receiving device that receives, from another node        apparatus, a route control message which includes information        required for determining a route on the network;    -   a distance receiving device that receives, from the distance        estimating apparatus, the distance up to the topology change        part;    -   a route computing device that determines the route on the        network based on the received route control message;    -   a message sending device that sends another node apparatus a        route control message which includes information required for        said another node apparatus to determine a route on the network;    -   a delay computing device wherein when receiving the route        control message by the message receiving device, the delay        computing device computes an operation start time for route        control operation executed by the route computing device and the        message sending device, based on the distance up to the topology        change part, which was received by the distance receiving        device; and    -   an execution control device that controls the execution of the        route control operation by the route computing device and the        message sending device, based on the operation start time        computed by the delay computing device.

In order to solve the above-described problem, the present inventionalso provides a route computation apparatus connected to at least onenode apparatus among node apparatuses wherein when a topology changeoccurs on a network used for packet transfer, the route computationapparatus performs dynamic route control for establishing a new normalroute, and the route computation apparatus comprises:

a message receiving device that receives, from said at least one nodeapparatus, a route control message which includes information requiredfor determining a route on the network;

a route computing device that determines the route on the network basedon the received route control message;

a message sending device that sends another node apparatus via said atleast one node apparatus, a route control message which includesinformation required for said another node apparatus to determine aroute on the network;

a delay computing device wherein when receiving the route controlmessage by the message receiving device, the delay computing devicecomputes an operation start time for route control operation executed bythe route computing device and the message sending device, based on adistance between a topology change part and said at least one nodeapparatus; and

an execution control device that controls the execution of the routecontrol operation by the route computing device and the message sendingdevice, based on the operation start time computed by the delaycomputing device.

Effect of the Invention

In accordance with the present invention, when a change in topologyoccurs on the network, it is possible to shorten the service stop timewithout damaging the stability of the network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of a node apparatus ofthe first embodiment of the present invention.

FIG. 2 is a flowchart for explaining a message receiving operation usinga route control protocol in the node apparatus of the first embodiment.

FIG. 3 is a schematic diagram showing the structure of each field of LSAheader for an OSPF message.

FIG. 4 is a schematic diagram showing the structure of each field ofRouter LSA for an OSPF message.

FIG. 5 is a schematic diagram showing the structure of each field ofNetwork LSA for an OSPF message.

FIG. 6 is a schematic diagram showing a tree structure obtainable in theroute computation of the first embodiment.

FIG. 7 is a flowchart explaining the procedure for measuring thedistance up to a damaged part based on OSPF in the first embodiment.

FIG. 8 is a block diagram showing the structure of a node apparatus ofthe second embodiment of the present invention.

FIG. 9 is a block diagram showing an example structure of the nodeapparatus 1′ and a damaged part estimating system 2 in the secondembodiment.

FIG. 10 is a flowchart explaining the message receiving operation basedon the route control protocol in the second embodiment.

FIG. 11 is a block diagram showing the structure of a node apparatus 10of the third embodiment of the present invention.

FIG. 12 is a block diagram showing the structure of a node apparatus 10′of the fourth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Below, embodiments of the present invention will be explained withreference to the drawings.

A. First Embodiment

A first embodiment of the present invention will be explained first.

FIG. 1 is a block diagram showing the structure of the node apparatus ofthe first embodiment of the present invention.

In the figure, a node apparatus 1 includes a route control unit 11 forperforming exchange of route information or the like between the nodeapparatus 1 and another node apparatus; a packet transfer unit 12 fortransferring each packet based on information in a route list preparedby the route control unit 11; a timer management unit 13 for managingeach timer used by the route control unit 11; a real time clock 14 forsecuring the present time; and network interfaces 21 to 2 n forconnecting to external networks 31 to 3 n.

The route control unit 11 includes a message receiver 111 for receivinga message for a route control protocol from another node apparatus; amessage sender 112 for sending a message for the route control protocolto another node apparatus when receiving an operation instruction from adelay operator 133; a route information database 113 for storing routeinformation obtained from another node apparatus via the messagereceiver 111; a route computer 114 for performing a route computationusing the route information stored in the route information database 113when receiving an operation instruction from the delay operator 133; anda delay computer 115. When the message receiver 111 receives a message,the delay computer 115 computes a time from the message reception to thestart of the route computation and a time from the message reception tothe transfer of the message to an adjacent node apparatus, by using atopology change part communicated by the message.

The packet transfer unit 12 includes a routing processor 121 forperforming an operation of transferring each packet received via thenetwork interfaces 21 to 2 n; and a main route list 122 having a tablefor determining the addressee and the network interface to be used forthe next transfer, based on the addressee of the relevant packet.

The timer management unit 13 includes a computation start delay timer131 for measuring a time t_(c), (i.e., timer value t_(c)) from themessage reception to the start of the route computation; a messagetransfer delay timer 132 for measuring a time t_(t) (i.e., timer valuet_(t)) from the message reception to the transfer of the receivedmessage to an adjacent node apparatus; and the delay operator 133. Whenreceiving a notification indicating that the time corresponding to thetimer value t_(c) or t_(t), set in the computation start delay timer 131or the message transfer delay timer 132, has elapsed, the delay operator133 issues an operation start instruction to the route computer 114 (fort_(c)) or the message sender 112 (for t_(t)).

In the first embodiment, the route control unit 11, the timer managementunit 13, and the real time clock 14 are provided in the node apparatus1. However, they may be provided in an apparatus separate from the nodeapparatus 1.

For example, a server apparatus separate from the node apparatus may beprovided, and the route control unit 11, the timer management unit 13,and the real time clock 14 may be contained in the server apparatus.

The node apparatus 1 and the server apparatus may be directly connectedvia a dedicated cable, or may be connected via any one of the networks31, 32, . . . , 3 n connected to the node apparatus 1.

Next, the operation of the first embodiment will be explained.

FIG. 2 is a flowchart for explaining a message receiving operation usinga route control protocol in the node apparatus 1 of the firstembodiment.

A message using the route control protocol is not only communicated whena topology change occurs due to a failure in a node apparatus or a linkas a constituent of the relevant network, but also used for monitoringan adjacent node apparatus.

The above message using the route control protocol indicates a messagefor communicating a topology change, and the following explanationrelates to the operation performed when receiving such a message.

First, arrival of a message sent from an adjacent node by using theroute control protocol is awaited using the message receiver 111 (seestep Sa1).

Next, the delay computer 115 computes a distance d between the presentnode and a damaged part by referring to the message of the route controlprotocol, which is received by the message receiver 111 (see step Sa2).The distance d is represented by the number (called “hop number”) of thenodes which are present on the shortest path from the present node tothe damaged part (at which the topology is changed).

The delay computer 115 uses values t_(ic) and t_(it), which arepredetermined by specific setting, so as to compute the timer valuet_(c) (=t_(ic)×d) set at the computation start delay timer 131 and thetimer value t_(t) (=t_(it)×d) set at the message transfer delay timer132 (see step Sa3).

Next, the delay computer 115 supplies the computed timer values t_(c)and t_(t) to the computation start delay timer 131 and the messagetransfer delay timer 132 so as to start the time measuring operation ofeach timer (see step Sa4).

When the time corresponding to the timer value t_(c) set at thecomputation start delay timer 131 has elapsed, the delay operator 133commands the route computer 114 to perform the route computation (seestep Sa5).

Additionally, when the time corresponding to the timer value t_(t) setat the message transfer delay timer 132 has elapsed, the delay operator133 commands the message sender 112 to perform the message transmission(see step Sa6).

The order for the execution of steps Sa5 and Sa6 may be exchanged inaccordance with the set timer values t_(c) and t_(t).

When the entire operation is completed, the operation returns to stepSa1, and the above-described steps are repeatedly executed.

In step Sa3, the timer values t_(c) and t_(t) are computed so that theyare each in proportion to the distance d. However, it is not an absolutecondition. The timer values t_(c) and t_(t) may each be in proportion tothe square of the distance d, or the distance d may be computed using afunction whose variable is the distance d.

Another computation method will be shown. The timer values t_(c) andt_(t) computed as described above are respectively comparedpredetermined upper limit values t_(cmax) and t_(tmax). If the latter(upper limit) is smaller, the upper limit (t_(cmax) or t_(tmax)) is usedas the corresponding timer value (t_(c) or t_(t)). That is, the upperlimits t_(cmax) and t_(tmax) are predetermined so as to pretend thetimer values t_(c) and t_(t) from being too great.

Such upper limit setting may be applied, not only to the timer valuest_(c) and t_(t), but also to the distance d. For example, if thedistance d used for a target computation is greater than a predeterminedupper limit d_(max), the upper limit d_(max) is preferably used insteadof the distance d, so as to compute the timer values t_(c) and t_(t).

In addition, the timer values t_(c) and t_(t) may be computed asfollows.

The timer values t_(c) and t_(t) computed by the delay computer 115 arerespectively compared with values which are predetermined by specificsetting. If the former values are greater, the timer values t_(c) andt_(t) are set to be infinite.

Setting the timer values t_(c) and t_(t) to be infinite means that thecomputation start delay timer 131 and the message transfer delay timer132 are not to be operated, and that the route computation by the routecomputer 114 and the retransfer by the message sender 112 are not to beexecuted.

In such a case, although the route computation or the like is notperformed, updated data (i.e., route information) communicated by thecurrently received route control message is effective in the routeinformation database 113. After that, when another route control messageis received and the timer values t_(c) and t_(t) computed by the delaycomputer 115 are not infinite, the route computation is performed whileconsidering the previously updated data. Also in the correspondingmessage transmission, the route control message which was not sent inthe previous transmission is sent simultaneously.

A similar operation can be performed for the upper limit d_(max) for thedistance d. If the distance d used for a target computation exceeds theupper limit d_(max), the timer values t_(c) and t_(t) are treated asinfinite values.

In addition, the computation method may be switched in accordance withwhether the distance d used for a target computation exceeds apredetermined threshold d_(th).

For example, when the distance d does not exceed the predeterminedthreshold d_(th), the timer values t_(c) and t_(t), each beingproportional to the distance d, are used, and otherwise, the timervalues, each being proportional to the square of the distance d, areused.

Instead of such a single threshold, a plurality of thresholds may beused. For example, two thresholds d_(th1), and d_(th2) (d_(th1)<d_(th2))may be used, and different methods may be assigned to the followingthree conditions for the distance d.d<d_(th1)  (1)d_(th1)≦d<d_(th2)  (2)d_(th2)≦d  (3)

Instead of employing the hop number, the distance d used in step Sa3 maybe represented by the sum of the cost values for the path between twonodes, that is, the sum of the cost values assigned to each node andeach link between the relevant nodes.

In the OSPF protocol, the cost value is assigned only to each link, andnot assigned to each node. In such a case, the sum of the cost values ofeach link on the path may be used as the total cost value for the path.

On the contrary, if the cost value is assigned only to each node and notassigned to each link, the sum of the cost values of each node on thepath may be used as the total cost value for the path.

Next, the process for computing the distance d in step Sa2 will beexplained in more detail.

In this process of the first embodiment, the route computer 114 in FIG.1 uses information for a tree structure generated during the routecomputation for ordinary OSPF. Therefore, the route computation for OSPFand information used therefor will be explained first.

Between the nodes within a network operated based on OSPF, informationexchange is performed using a unit called “LSA (link stateadvertisement)” for the route computation. FIGS. 3 to 5 are schematicdiagrams showing popular packet formats for LSA.

FIG. 3 shows a format of a part which is called “LSA header” in an OSPFmessage, and is commonly used regardless of the type of LSA.

FIG. 4 shows a packet format of “Router LSA” for an OSPF message. Thispart is located immediately after LSA header shown in FIG. 3.

For Router LSA, a value 1 for indicating that the present LSA is aRouter LSA is stored in a field 42 (see “Link State Type”) in FIG. 3.

In a field 43 (see “Link State ID”) of FIG. 3, an individual number(called “Router ID”) assigned to each node apparatus (i.e., router) isstored.

As shown in FIG. 4, in the part located immediately after LSA header,fields 53 to 57 form a group, where information about a link connectedto the relevant node apparatus is stored.

When a plurality of links are connected to the node apparatus, similarinformation is stored in fields from a field 58 and after.

As described above, Router LSA indicates which link the relevant nodeapparatus (i.e., router) is connected to.

Next, FIG. 5 shows a packet format of “Network LSA” for an OSPF message.This part is also located immediately after LSA header shown in FIG. 3.

For Network LSA, a value 2 for indicating that the present LSA is aNetwork LSA is stored in the field 42 (see “Link. State Type”) in FIG.3.

In the field 43 (see “Link State ID”) of FIG. 3, an ID (called “RouterID”) for identifying a representative node apparatus (i.e., router)among the node apparatuses (routers) connected to the relevant link,which is called a “designated router”, is stored.

In fields 71 to 7 n (see “Attached Router 1 to Attached Router n”) ofFIG. 5, Router IDs of the node apparatuses connected to the present linkare stored.

As described above, Network LSA indicates whether a target router isconnected to the present link.

The route computation of OSPF uses topology information obtained byjoining the collected information items about Router LSA and Network LSAtogether. A Dijkstra's algorithm used for solving a shortest pathproblem is applied to the topology information so as to determine theshortest path.

FIG. 6 is a schematic diagram showing a tree structure obtainable in theroute computation of the first embodiment.

In the relevant computation, information having a tree structure asshown in FIG. 6 can be obtained, where Router LSA indicating oneself islocated at the head (L11) of the tree.

In the first embodiment, the information having such a tree structure isused for computing the distance d from the damaged part to the nodeapparatus 1.

FIG. 7 is a flowchart explaining the procedure for measuring thedistance d up to a damaged part based on OSPF in the first embodiment.

First, information about a tree structure obtained in the routecomputation performed by the route computer 114 is sent to the delaycomputer 115 (see step Sb1). This step indicates that information abouta tree structure obtained in the route computation performed immediatelybefore is used to determine the tinier values t_(c) and t_(t) used forthe next route computation and message transmission.

Next, LSA in the received message is referred to, so as to examine thecorresponding position of the relevant LSA in the tree structure (seestep Sb2).

The next step examines how many Router LSAs are present between the LSAfound in step Sb2 on the tree structure and the root of the tree (seestep Sb3).

The value obtained in step Sb3 is added to 1, and the sum is determinedto be the distance d (see step Sb4).

In an example case which will be explained below, a failure has occurredbetween Router (LSA) L53 and Network (LSA) L61 connected thereto.

In such a case, since the node apparatus represented by Router (LSA) L53has no connection with a link represented by Network (LSA) L61, Router(LSA) L53 is updated and relevant information is communicated to eachnode apparatus.

When a node apparatus which manages the information about the treestructure shown in FIG. 6 receives the communicated information, thenode apparatus examines the number of Route (LSA)s present betweenRouter (LSA) L53 and Network (LSA) L11.

Since only Router (LSA) L34 satisfies the above condition, the value 1is added to 1, so that the distance “2” is obtained.

Although OSPF as a route control protocol of IPv4 is employed in thefirst embodiment, operation on a similar method can be applied to routecontrol of IPv6.

In accordance with the above-described first embodiment, a timer valuedepending on the distance from a damaged part to the present nodeapparatus is supplied to a timer used for preventing an increase in therelevant load. Therefore, a relatively small timer value is applied to anode apparatus close to the damaged part, thereby reducing the servicestop time. In addition, since a relatively large timer value is appliedto a node apparatus far away from the damaged part, it is possible toprevent the load for the route computation from increasing temporarily,and to improve the stability of the network.

In the above method, the load for the route computation of a nodeapparatus close to the damaged part may be larger than that forconventional methods. However, an average load for the route computationin the entire network can be reduced.

B. Second Embodiment

Next, a second embodiment of the present invention will be explained.

FIG. 8 is a block diagram showing the structure of a node apparatus ofthe second embodiment of the present invention.

In the figure, in comparison with the structure (see FIG. 1) of thefirst embodiment, the second embodiment has a distinctive feature ofhaving a damaged part information receiver 116.

In a path-vector route control protocol such as BGP, a prefix iscommunicated together with an AS (autonomous system) path. When a linkfailure or the like occurs, a substitute route is communicated togetherwith a new path. However, the damaged part cannot be detected only basedon the communicated information.

Here, a technique for estimating a damaged part based on some kind ofinformation has been examined and developed, as shown in ReferenceDocument 1 (Atsuo Tachibana, Shigehiro Ano, and Masato Tsuru, “Aproposal of Locating BGP Routing Failures based on Simulation Analysis”,Meeting of IEICE Communications Society, B-16-6, p. 134, 2008).

Accordingly, a node apparatus 1′ in the second embodiment receives, bymeans of the damaged part information receiver 116, a notificationindicating information about a damaged part estimated by a damaged partestimating system explained below. The timer values t_(c) and t_(t) aredetermined based on the received information.

FIG. 9 is a block diagram showing an example structure of the nodeapparatus 1′ and a damaged part estimating system 2 in the secondembodiment.

In FIG. 9, the node apparatus 1′ and the damaged part estimating system2 are connected via an internal network 4 within an autonomous system,where each operation between the node apparatus 1′ and the damaged partestimating system 2 is performed within the autonomous system. Thedamaged part estimating system 2 is also connected to an externalnetwork 5 via the internal network 4 or the node apparatus 1′.

The damaged part estimating system 2 in FIG. 9 has a damaged partestimator 210 for estimating a damaged part, and a damaged partcommunicator 220 for communicating the damaged part estimated by thedamaged part estimator to the node apparatus 1′.

FIG. 10 is a flowchart explaining the message receiving operation basedon the route control protocol in the second embodiment.

In FIG. 10, steps Sc1, Sc5, Sc6, Sc7, and Sc8 are identical to Sa1, Sa3,Sa4, Sa5, and Sa6 in FIG. 2 for the operation of the above-describedfirst embodiment, and new steps Sc2 and Sc3 are inserted between stepsSc1 to Sc4 while the operation in step Sc4 (corresponding to step Sa2 inFIG. 2) is partially modified.

In step Sc2, the damaged part estimating system 2 estimates a damagedpart based on a message received from an adjacent node, and informs thenode apparatus 1′ of the estimated result.

In the next step Sc3, the damaged part information receiver 116 of thenode apparatus 1′ awaits arrival of information about the estimateddamaged part from the damaged part estimating system 2.

In the next step Sc4, the delay computer 115 computes distance d betweenthe present node and the damaged part communicated by the damaged partinformation receiver 116.

Instead of employing the hop number of nodes as the distance d in thefirst embodiment, the distance d used in the second embodiment may berepresented by the number of AS paths on the relevant route.

In the second embodiment, the damaged part is estimated using thedamaged part estimating system 2 which is an external system. Thedistance up to the damaged part may be computed using an externalsystem. In such a case, the node apparatus 1′ of the second embodimentmay receive a distance d from the external system to the damaged part,and compute the timer values t_(c) and t_(t) used for the route control,based on the received distance d

In accordance with the above-described second embodiment, a damaged partor a distance up to the damaged part is estimated using the distancedamaged part estimating system 2 which is an external system, and thenode apparatus 1′ computes the timer values t_(c) and t_(t) used for theroute control, based on the damaged part or the distance up to thedamaged part received from the distance damaged part estimating system2. Therefore, the load relating to the route control can be furtherreduced, thereby further improving the stability of the network.

C. Third Embodiment

Next, a third embodiment of the present invention will be explained.

FIG. 11 is a block diagram showing the structure of a node apparatus 10of the third embodiment of the present invention.

In the figure, in comparison with the structure (see FIG. 1) of thefirst embodiment, the third embodiment has a delay manager 134.

In the third embodiment, during the operation of the computation startdelay timer 131 or the message transfer delay timer 132, an additionalstep relating to the message reception by the route control protocol isperformed.

Similar to the above-described first embodiment, the delay computer 115determines the timer value k up to the start of the route computationand the timer value t_(t) up to the start of the message retransfer, andsends the timer values to the delay manager 134.

The delay manager 134 compares the timer value t_(c) up to the start ofthe route computation (sent from the delay computer 115) with thecurrent value at the computation start delay timer 131.

If the timer value t_(c) up to the start of the route computation issmaller, the computation start delay timer 131 is updated using thetimer value t_(c).

Similarly, the delay manager 134 compares the tinier value t_(t) up tothe start of the message retransfer (sent from the delay computer 115)with the current value at the message transfer delay timer 132. If thetimer value t_(t) is smaller, the message transfer delay timer 132 isupdated using the tinier value t_(t).

In accordance with the above-described third embodiment, a case in whicha change in the network topology occurs at a plurality of parts can alsobe handled.

D. Fourth Embodiment

Next, a fourth embodiment of the present invention will be explained.

FIG. 12 is a block diagram showing the structure of a node apparatus 10′of the fourth embodiment of the present invention.

In the figure, in comparison with the structure (see FIG. 1) of thefirst embodiment, the fourth embodiment has a route updating start delaytimer 135 in place of the computation start delay timer 131 and themessage transfer delay timer 132.

In the fourth embodiment, the delay computer 115 computes a timer valuet_(r) up to the start of route updating by using a method similar tothat of the first embodiment, and supplies the computed value to theroute updating start delay timer 135.

When the timer value t_(r) is set at the route updating start delaytimer 135, the timer 315 starts countdown operation, which continuesuntil the timer value t_(r) decreases to zero.

When the value of the route updating start delay timer 135315 becomeszero, the delay operator 133 commands the route computer 114 to startupdating the main route list 122 by using the route obtained by theroute computation.

In accordance with the fourth embodiment, degradation in stability ofthe network due to instability in the operation of the packet transferunit 12 during the updating of the relevant route list can be spatiallyand temporally distributed by delaying the updating itself of the mainroute list 122, thereby further improving the stability of the network.

INDUSTRIAL APPLICABILITY

As a specifically anticipated example of an application of the presentinvention, the present invention can be applied to a high availabilityrouter on a carrier's IP backbone network.

Reference Symbols

-   1, 1′, 10, 10′ node apparatus-   11 route control unit-   12 packet transfer unit-   13 timer management unit-   14 real time clock-   21 to 2 n network interface-   31 to 3 n external network-   111 message receiver-   112 message sender-   113 route information database-   114 route computer-   115 delay computer-   116 damaged part information receiver-   121 routing processor-   122 main route list-   131 computation start delay timer-   132 message transfer delay timer-   133 delay operator-   134 delay manager-   135 route updating start delay timer-   2 damaged part estimating system-   210 damaged part estimator-   220 damaged part communicator-   4 internal network-   5 external network

The invention claimed is:
 1. A node apparatus wherein when a topologychange occurs on a network used for packet transfer between nodeapparatuses, said node apparatus performs dynamic route control forestablishing a new normal route, and said node apparatus comprises: amessage receiving device that receives, from another node apparatus, aroute control message which includes information required for routedetermination; a route computing device that determines a route on thenetwork based on the received route control message; a message sendingdevice that sends another node apparatus a route control message whichincludes information required for said another node apparatus todetermine a route on the network; a delay computing device wherein whenreceiving the route control message by the message receiving device, thedelay computing device computes an operation start time for routecontrol operation executed by the route computing device and the messagesending device, based on a distance between a topology change part andsaid node apparatus of oneself; and an execution control device thatcontrols the execution of the route control operation by the routecomputing device and the message sending device, based on the operationstart time computed by the delay computing device.
 2. The node apparatusin accordance with claim 1, wherein: the execution control device has acomputation start delay timer device that measures a time up to thestart of the route computation by the route computing device, based onthe operation start time computed by the delay computing device.
 3. Thenode apparatus in accordance with claim 2, wherein: the executioncontrol device has a delay operation device; and when the time measuredby the computation start delay timer device reaches the operation starttime, the delay operation device commands the route computing device tostart the route computation.
 4. The node apparatus in accordance withclaim 1, wherein: the execution control device has a message transferdelay timer device that measures a time up to the start of the routecontrol message sending by the message sending device, based on theoperation start time computed by the delay computing device.
 5. The nodeapparatus in accordance with claim 4, wherein: the execution controldevice has a delay operation device; and when the time measured by themessage transfer delay timer device reaches the operation start time,the delay operation device commands the message sending device to startthe route control message sending.
 6. The node apparatus in accordancewith claim 1, wherein: the delay computing device uses the hop number,which is the number of nodes present between the topology change partand said node apparatus of oneself, as the distance used for computingthe operation start time.
 7. The node apparatus in accordance with claim1, wherein: the delay computing device uses the sum of costs for a pathbetween the topology change part and said node apparatus of oneself, asthe distance used for computing the operation start time.
 8. The nodeapparatus in accordance with claim 1, wherein: the delay computingdevice uses the number of autonomous systems present between thetopology change part and said node apparatus of oneself, as the distanceused for computing the operation start time.
 9. The node apparatus inaccordance with claim 1, wherein: the delay computing device uses ashortest path tree generated during the route computation by the routecomputing device, so as to determine the distance used for computing theoperation start time.
 10. The node apparatus in accordance with claim 1,wherein: the delay computing device determines a distance computed andcommunicated by an external system, to be the distance used forcomputing the operation start time.
 11. The node apparatus in accordancewith claim 1, wherein: the delay computing device obtains the topologychange part used for obtaining the distance, from the route controlmessage received by the message receiving device.
 12. The node apparatusin accordance with claim 1, wherein: the delay computing device obtainsthe topology change part used for obtaining the distance, frominformation determined and communicated by an external system.
 13. Thenode apparatus in accordance with claim 1, wherein: the delay computingdevice determines a value proportional to the distance between atopology change part and said node apparatus of oneself to be theoperation start time for the route control operation by the routecomputing device and the message sending device.
 14. The node apparatusin accordance with claim 1, wherein: the delay computing device computesthe operation start time for the route control operation by the routecomputing device and the message sending device, by using a computationmethod determined in accordance with a result of comparison between thedistance up to the topology change part and a predetermined value. 15.The node apparatus in accordance with claim 14, wherein: when the resultof the comparison indicates that the distance up to the topology changepart is larger than the predetermined value, the delay computing deviceuses the predetermined value as the distance so as to compute theoperation start time for the route control operation by the routecomputing device and the message sending device.
 16. The node apparatusin accordance with claim 14, wherein: when the result of the comparisonindicates that the distance up to the topology change part is largerthan the predetermined value, the delay computing device sets theoperation start time for the route control operation by the routecomputing device and the message sending device to be infinite.
 17. Thenode apparatus in accordance with claim 1, wherein: the delay computingdevice compares the computed operation start time with a predeterminedvalue, and sets the operation start time to the predetermined value ifthe computed operation start time is larger than the predeterminedvalue.
 18. The node apparatus in accordance with claim 17, wherein: thedelay computing device determines the computed operation start time tobe effective only when a result of the comparison indicates that thecomputed operation start time is smaller than the predetermined value.19. The node apparatus in accordance with claim 1, wherein: theexecution control device has a route updating start delay timer devicethat measures, based on the operation start time computed by the delaycomputing device, a time up to the start of updating a route list byusing the route computed by the route computing device, where the routelist contains route information on the network used for the packettransfer.
 20. The node apparatus in accordance with claim 19, wherein:the execution control device has a delay operation device; and when thetime measured by the route updating start delay timer device reaches theoperation start time, the delay operation device commands the routecomputing device to start the updating of the route list.
 21. The nodeapparatus in accordance with claim 2, wherein: the execution controldevice has a delay managing device; and if the timer device is operatingwhen the route control message is newly received by the messagereceiving device, then the delay managing device controls updating ofthe time measured by the timer device which is operating, based on aresult of comparison between the operation start time computed by thedelay computing device and the time measured by the timer device. 22.The node apparatus in accordance with claim 3, wherein: the delaycomputing device uses the hop number, which is the number of nodespresent between the topology change part and said node apparatus ofoneself, as the distance used for computing the operation start time,where the topology change part is obtained from the route controlmessage received by the message receiving device.
 23. A route controlmethod wherein when a topology change occurs on a network used forpacket transfer between node apparatuses, the method is used forestablishing a new normal route, and said method comprises: a receivingstep that receives a route control message which includes informationrequired for determining a route on the network; a route computing stepthat determines the route on the network based on the received routecontrol message; a sending step that sends a node apparatus a routecontrol message which includes information required for said nodeapparatus to determine a route on the network; a delay computing stepwherein when receiving the route control message, the delay computingstep computes an operation start time for the determination of the routeon the network and the sending of the route control message, based on adistance between a topology change part and a node apparatus of oneself;and an execution control step that controls the execution of the routedetermination and the route control message sending, based on thecomputed operation start time.
 24. The route control method inaccordance with claim 23, wherein: the execution control step has acomputation start time measuring step that measures a time up to thestart of the route determination, based on the operation start time. 25.The route control method in accordance with claim 23, wherein: theexecution control step has a message transfer start time measuring stepthat measures a time up to the start of the route control messagesending, based on the operation start time.
 26. The route control methodin accordance with claim 23, wherein: the delay computing step uses thehop number, which is the number of nodes present between the topologychange part and said node apparatus of oneself, as the distance used forcomputing the operation start time.
 27. The route control method inaccordance with claim 23, wherein: the delay computing step uses the sumof costs for a path between the topology change part and said nodeapparatus of oneself, as the distance used for computing the operationstart time.
 28. The route control method in accordance with claim 23,wherein: the delay computing step uses the number of autonomous systemspresent between the topology change part and said node apparatus ofoneself, as the distance used for computing the operation start time.29. The route control method in accordance with claim 23, wherein: thedelay computing step uses a shortest path tree generated by the routecomputing step, so as to determine the distance used for computing theoperation start time.
 30. The route control method in accordance withclaim 23, wherein: the delay computing step determines a distancecomputed and communicated by an external system, to be the distance usedfor computing the operation start time.
 31. The route control method inaccordance with claim 23, wherein: the delay computing step obtains thetopology change part used for obtaining the distance, from the routecontrol message received by the receiving step.
 32. The route controlmethod in accordance with claim 23, wherein: the delay computing stepobtains the topology change part used for obtaining the distance, frominformation determined and communicated by an external system.
 33. Theroute control method in accordance with claim 23, wherein: the delaycomputing step determines a value proportional to the distance between atopology change part and said node apparatus of oneself to be theoperation start time for the route determination and the route controlmessage sending.
 34. The route control method in accordance with claim23, wherein: the delay computing step computes the operation start timefor the route determination and the route control message sending, byusing a computation method determined in accordance with a result ofcomparison between the distance up to the topology change part and apredetermined value.
 35. The route control method in accordance withclaim 34, wherein: when the result of the comparison indicates that thedistance up to the topology change part is larger than the predeterminedvalue, the delay computing step uses the predetermined value as thedistance so as to compute the operation start time for the routedetermination and the route control message sending.
 36. The routecontrol method in accordance with claim 34, wherein: when the result ofthe comparison indicates that the distance up to the topology changepart is larger than the predetermined value, the delay computing stepsets the operation start time for the route determination and the routecontrol message sending to be infinite.
 37. The route control method inaccordance with claim 23, wherein: the delay computing step compares thecomputed operation start time with a predetermined value, and sets theoperation start time to the predetermined value if the computedoperation start time is larger than the predetermined value.
 38. Theroute control method in accordance with claim 37, wherein: the delaycomputing step determines the computed operation start time to beeffective only when a result of the comparison indicates that thecomputed operation start time is smaller than the predetermined value.39. The route control method in accordance with claim 23, wherein: theexecution control step has a route updating start time measuring stepthat measures, based on the operation start time computed by the delaycomputing step, a time up to the start of updating a route list by usingthe route computed by the route computing step, where the route listcontains route information on the network used for the packet transfer.40. The route control method in accordance with claim 24, wherein: theexecution control step has a delay managing step; and if the timemeasuring step is being executed when the route control message is newlyreceived by the receiving step, then the delay managing step comparesthe operation start time computed by the delay computing step using thenew route control message with the time measured by the time measuringstep which is being executed, and controls updating of the time measuredby the time measuring step, based on a result of the comparison.
 41. Aroute computation system which operates in an autonomous system, andincludes a node apparatus and a damaged part estimating apparatus whichare connected via an internal network within the autonomous system,wherein: when a topology change occurs on a network used for packettransfer between node apparatuses, the route computation system performsdynamic route control for establishing a new normal route; the damagedpart estimating apparatus comprises: a damaged part estimating devicethat estimates a topology change part; and a damaged part communicatingdevise that communicates the topology change part estimated by thedamaged part estimating device to the node apparatus; and the nodeapparatus comprises: a message receiving device that receives, fromanother node apparatus, a route control message which includesinformation required for determining a route on the network; a damagedpart receiving device that receives the topology change part from thedamaged part estimating apparatus; a route computing device thatdetermines the route based on the received route control message; amessage sending device that sends another node apparatus a route controlmessage which includes information required for said another nodeapparatus to determine a route on the network; a delay computing devicewherein when receiving the route control message by the messagereceiving device, the delay computing device computes an operation starttime for route control operation executed by the route computing deviceand the message sending device, based on a distance between the nodeapparatus of oneself and the topology change part received by thedamaged part receiving device; and an execution control device thatcontrols the execution of the route control operation by the routecomputing device and the message sending device, based on the operationstart time computed by the delay computing device.
 42. A routecomputation system which operates in an autonomous system, and includesa node apparatus and a distance estimating apparatus which are connectedvia an internal network within the autonomous system, wherein: when atopology change occurs on a network used for packet transfer betweennode apparatuses, the route computation system performs dynamic routecontrol for establishing a new normal route; the distance estimatingapparatus comprises: a distance estimating device that estimates adistance between the node apparatus and a topology change part; and adistance communicating devise that communicates the distance estimatedby the distance estimating device to the node apparatus; and the nodeapparatus comprises: a message receiving device that receives, fromanother node apparatus, a route control message which includesinformation required for determining a route on the network; a distancereceiving device that receives, from the distance estimating apparatus,the distance up to the topology change part; a route computing devicethat determines the route on the network based on the received routecontrol message; a message sending device that sends another nodeapparatus a route control message which includes information requiredfor said another node apparatus to determine a route on the network; adelay computing device wherein when receiving the route control messageby the message receiving device, the delay computing device computes anoperation start time for route control operation executed by the routecomputing device and the message sending device, based on the distanceup to the topology change part, which was received by the distancereceiving device; and an execution control device that controls theexecution of the route control operation by the route computing deviceand the message sending device, based on the operation start timecomputed by the delay computing device.
 43. A route computationapparatus connected to at least one node apparatus among nodeapparatuses wherein when a topology change occurs on a network used forpacket transfer, the route computation apparatus performs dynamic routecontrol for establishing a new normal route, and the route computationapparatus comprises: a message receiving device that receives, from saidat least one node apparatus, a route control message which includesinformation required for determining a route on the network; a routecomputing device that determines the route on the network based on thereceived route control message; a message sending device that sendsanother node apparatus via said at least one node apparatus, a routecontrol message which includes information required for said anothernode apparatus to determine a route on the network; a delay computingdevice wherein when receiving the route control message by the messagereceiving device, the delay computing device computes an operation starttime for route control operation executed by the route computing deviceand the message sending device, based on a distance between a topologychange part and said at least one node apparatus; and an executioncontrol device that controls the execution of the route controloperation by the route computing device and the message sending device,based on the operation start time computed by the delay computingdevice.